“That’s queer,” spoke Tom.

“Very,” agreed Ned.  “He didn’t go back after all.  I’d like to know what’s going on in there.”

“And there’s someone else who would like to know, also, I think,” said Tom in a low voice.

“Who?” asked Ned.

“That man hiding behind the big tree across the street.  I’m sure he’s watching the Foger house, and when Andy came to the door that time, I happened to look around and saw that man focus a pair of opera glasses on him and the carpenter.”

“You don’t mean it, Tom!” exclaimed Ned.

“I sure do.  I believe that man is some sort of a spy or a detective.”

“Do you think he’s after Andy?”

“I don’t know.  Let’s not get mixed up in the affair, anyhow.  I don’t want to be called in as a witness.  I haven’t the time to spare.”

As if the man behind the tree was aware that he had attracted the attention of our friends, he quickly turned and walked away.  Tom and Ned glanced up at the Foger house, but saw nothing, and proceeded on to the store.

“I’ll wager anything that Andy has been getting in some sort of trouble in the town he moved to from here,” went on Tom, “and he daren’t go back.  So he came here, and he’s hiding in his father’s old house.  He could manage to live there for a while, with the carpenter bringing him in food.  Say, did you notice who that man was, with the saw?”

“Yes, he’s James Dillon, a carpenter who lives down on our street,” replied Ned.  “A nice man, too.  The next time I see him, I’m going to ask him what Andy is doing in town, and what the repairs are that he’s making on the house.”

“Well, of course if Andy has been doing anything wrong, he wouldn’t admit it,” said Tom.  “Though Mr. Dillon may tell you about the carpenter work.  But I’m sure that man was a detective from the town where Andy moved to.  You’ll see.”

“I don’t think so,” was Ned’s opinion.  “If Andy was hiding he wouldn’t show himself as plainly as he did.”

The two chums argued on this question, but could come to no decision.  Then, having reached Tom’s home with the bolts, they went hard at work on the airship.

“Well, now to see what happens!” exclaimed Tom the next day, when everything was ready for a trial flight.  “I wish Mr. Damon was here.  I sent him word, but I didn’t hear from him.”

“Oh, he may show up any minute,” replied Ned, as he helped Tom and Koku wheel the newly-equipped airship out of the shed.  “The first thing you’ll hear will be him blessing something.  Is this far enough out, Tom?”

“No, a little more, and then head her up into the wind.  I say, Ned, if this is a success, and—­”

Tom stopped suddenly and looked out into the road.  Then, in a low voice, he said, to Ned: 

“Don’t move suddenly, or he’ll suspect that we’re onto his game, but turn around slowly, and look behind that big sycamore tree in front of our house Ned.  Tell me what you see.”